Proposal to return to Roman concrete to make the construction industry more sustainable

This article is interesting and of good quality, and you can learn from it if you are familiar with the subject, but for people outside the field of concrete, it may raise somewhat exaggerated expectations. To begin with, the formulation of Roman concrete is well known because it has been recorded in writing. We do indeed know that it is a more durable concrete than those commonly used today, but also that it is less resistant, takes longer to set, depends on components (such as volcanic ash) that are not easily obtainable everywhere, and in some of its most striking uses (I am referring to mixtures with seawater) is incompatible with the steel reinforcement that is essential in our reinforced and prestressed concrete structures.

We have already learned the lessons of Roman concrete, so much so that similar concretes can be manufactured in accordance with regulations that allow the use of ash additives; in fact, they are commonly used in structures with special durability requirements, and their drawbacks are taken into account in the design.

All studies that contribute to the decarbonisation of cement (a very real problem and well addressed in the article) are welcome, but today there are much more promising lines of research into so-called “green cements”, using other industrial by-products such as blast furnace bottom ash or waste from the timber industry.

The work on the sustainability of Roman mortars and concretes is based on a serious, high-quality study. Furthermore, the conclusions drawn by the authors are based on objective data. What is more, the limitations of the study and the difficulty of transferring certain aspects of the construction of this type of material to the present day are well founded. The main drawback of the article is that when reading the highlights, it seems that the use of Roman mortars and concretes was much more sustainable than the use of modern mortars and concretes; however, when reading the article, this aspect is much better explained and the specific cases in which this could occur are evaluated.

The main implications or conclusions of the study, which are clearly accurate based on recent knowledge, are that the use of what are now called ‘alternative materials’ to Portland cement, such as biomass used in Roman mortars and concretes, clearly reduces the carbon footprint of the resulting material. However, the current use of these low-carbon materials should not limit the properties of concrete. The second key aspect addressed in the article is that the durability of construction materials, and therefore of the structures built, goes hand in hand with sustainability. In other words, ensuring high durability in a structure or building will be more sustainable in the long run due to lower resource consumption than if the building has to be demolished and rebuilt or if there are high maintenance costs, among other aspects. In this sense, it is true that Roman concrete has shown high durability over time, as in many cases it has remained almost intact to this day, although the durability of a structure will always be influenced by the use to which it is put. Could Roman concrete be used for the construction of large skyscrapers? It is very unlikely, but this is made clear in the article.